Yttrium oxide, which is a compound having a high melting point, has an excellent stability under a high temperature. Such yttrium oxide is potentially useful as a high temperature structural material or as translucent ceramics material.
However, yttrium oxide has not yet been put into practical usage as a structural material, due to its inferior mechanical properties as compared with currently available oxide ceramics such as aluminum oxide (Al.sub.2 O.sub.3) or zirconium oxide (ZrO.sub.2). Various approaches have been made to improve its strength by adding an additive to a sintered body mainly composed of yttrium oxide. According to a study made by the inventors of the present application, it has been recognized that the strength of a sintered body having a matrix of yttrium oxide can be improved by dispersing silicon carbide (SiC) therein. The result of this experiment has been reported by the inventors in Fourth Autumn Symposium, Ceramics Society of Japan, 1991.
However, when silicon carbide is simply dispersed in an yttrium oxide matrix, the flexural strength (fracture strength) of the resulting sintered body is at the level of 300 MPa at the utmost. This level is not sufficient for practical usage of a sintered body mainly composed of yttrium oxide available as structural ceramics.